How serious can it be to have blood in your stools? on and off for the last 7 years..?

Not normal....: You need to see a GI doctor to find out exactly why you have blood in your stools. It is likely benign since you have had it on and off for 7 years-possibly hemorrhoids which can be internal or even a fissure. But, there are more serious possibilities, like inflammatory bowel diseases that would need treating. So, see a GI specialist and get this diagnosed and treated. Good luck!

Seek medical care: other factors such as family history (of inflammatory conditions and cancer), environmental exposure, and symptoms (associated fevers, diarrhea, constipation, etc. need to be factored), but you should seek medical advice from your primary care physician to see if workup (most likely at a minimum a flexible sigmoidoscopy to assess for cause of recurrent bleeding, or full colonoscopy) is warranted